A long cylinder of 30-min diameter, initially at a uniform temperature of 1000 K, is suddenly quenched in a large, constant-temperature oil bath at 350 K. The cylinder properties are
(a) Calculate the time required for the surface of the cylinder to reach 500 K.
(b) Compute and plot the surface temperature history for
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Introduction to Heat Transfer
- 3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the atmosphere from outer space. If its original temperature is 38°C, the effective average temperature of the atmosphere is 1093°C, and the effective heat transfer coefficient is , estimate the temperature of the shell after reentry, assuming the time of reentry is 10 min and the interior of the shell is evacuated.arrow_forwardThe air-conditioning system in a Chevrolet van for use in desert climates is to be sized. The system is to maintain an interior temperature of 20C when the van travels at 100 km/h through dry air at 30C at night. If the top of the van is idealized as a flat plate 6 m long and 2 m wide and the sides as flat plates 3 m tall and 6 m long, estimate the rate at which heat must be removed from the interior to maintain the specifiedarrow_forwardAn electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.arrow_forward
- A spherical object with a temperature of 700 oC, made of carbon steel with a diameter of 3 cm, will be cooled to 370 oC by an air flow with a temperature of 35 oC and a heat convection coefficient of 90 W/m2K. Calculate the time (s) required to cool the body, ignoring the temperature gradient inside the body and making any other assumptions you deem necessary. The heat transmission coefficient of carbon steel can be 45 W/mK, its density is 7800 kg/m3 and its specific heat is 480 J/kgK.arrow_forwardA thermocouple junction, which may be approximated as a sphere, is to be used for temperature measurement in a gas stream. The convection coefficient between the junction surface and the gas is h=400W/m².K, and the junction thermophysical properties are ĸ= 20W/m.°K, c= 400J/kg.°K and ρ=8500kg/m³. Determine the junction diameter needed for the thermocouple to have a time constant of 1s. If the junction is at 25°C and is placed in a gas stream that is at 200°C, how long will it take for the junction to reach 199°C?arrow_forwardcylindrical fuel element for a gas-cooled nuclear reactor, the heat generation rate within the fuel element due to fission can be approximated by the relation: q(r) = q_0 [1 - (r/a)^2] W/m^3 where a is the radius of the fuel element and q_0 is constant. The boundary surface at r = a is maintained at a uniform temperature T_0. Assuming one-dimensional, steady-state heat flow, develop a relation for the temperature drop from the centerline to the surface of the fuel element. For radius a= 30mm, the thermal conductivity k = 10 W/m middot K and q_0 = 2 times 10^7 W/m^3, calculate the temperature drop from the centerline to the surface.arrow_forward
- A fabricated food, in the form of small spherical pellets, is to be frozen in an air-blast freezer. The air-blast freezer isoperating with air at -40°C. The initial product temperatureis 25°C. The pellets have a diameter of 0.5 cm, and the density of the product is 980 kg/m3. The initial freezing temperature is -2.5°C. The latent heat of fusion for this product is 280 kJ/kg. The thermal conductivity of the frozen productis 1.9 W/(m°C). The convective heat transfer coefficient is 50 W/(m2 °C). Calculate the freezing time.arrow_forwardPartially-frozen ice cream is being placed in a package before completion of the freezing process. The package has dimensions of 8 cm by 10 cm by 20 cm and is placed in air- blast freezing with convective heat coefficient of 50 W/(m2 K) for freezing. The product temperature is -5°C when placed in the package, and the air temperature is -25°C. The product density is 700 kg/m3, the thermal conductivity (frozen) is 1.2 W/(m K), and the specific heat of the frozen product is 1.9 kJ/(kg K). If the latent heat to be removed during blast freezing is 100 kJ/kg, estimate the freezing time.arrow_forwardA fabricated food, in the form of small spherical pellets, is to be frozen in an air-blast freezer. The air-blast freezer is operating with air at -30°C. The initial product temperature is 25°C. The pellets have a diameter of 1.2 cm, and the density of the product is 980 kg/m3 . The initial freezing temperature is -2.5°C. The latent heat of fusion for this product is 280 kJ/kg. The thermal conductivity of the frozen product is 1.9 W/(m°C). The convective heat transfer coefficient is 50 W/(m2°C). Calculate the freezing time.arrow_forward
- A fabricated food, in the form of small spherical pellets, is to be frozen in an air-blast freezer. The air-blast freezer is operating with air at -30°C. The initial product temperature is 25°C. The pellets have a diameter of 1.2 cm, and the density of the product is 980 kg/m³ . The initial freezing temperature is -2.5°C. The latent heat of fusion for this product is 280 kJ/kg. The thermal conductivity of the frozen product is 1.9 W/(m°C). The convective heat transfer coefficient is 50 W/(m² °C). Calculate the freezing time (h)arrow_forwardA small copper wire with a diameter of 0.792 mm and initially at 366.5 K is suddenly immersed in a liquid held constant at 311 K. The convection coefficient h = 85.2 W/m2 · K. The physical properties can be assumed constant and are k = 374 W/m · K, cp = 0.389 kJ/kg · K, and ρ = 8890 kg/m3. Determine the time in seconds for the average temperature of the wire to drop to 338.8 K (one-half the initial temperature difference). Do the same but for h=11.36W/m2·K. Forpart(b),calculate the total amount of heat removed for a wire 1.0 m long.arrow_forwardA 60 mm thickness large steel plate (k=42.6 W/m deg C, alpha = 0.043 m^2/h), initially at 440 deg C is suddenly exposed on both sides to an environment with convective heat transfer coefficient 235 W/m^2 deg C, and temperature 50 deg C. Determine the center line temperature, and temperature inside the plate 15 mm from the mid-plane after 4.3 minutes.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning